BSC2086 Anatomy & Physiology II Exam #1 Study Guide 1 Lesson 1: General Senses Sensory Information • Afferent division of the nervous system involves: o Receptors – detect the stimuli o Sensory neurons – relay the info down their axons o Sensory pathways – nerves, nuclei, & tracts that deliver sensory info to the CNS • Efferent division of the nervous system involves: o Nuclei – contain the cell bodies of motor neurons o Motor tracts & nerves – carry commands to effectors (muscles & glands) • Sensory Receptors: Specialized cells that monitor specific conditions in the body or external environment o Passes information (as action potentials along the axon of a sensory neuron) to the CNS when stimulated • Sensory Pathways: Deliver somatic & visceral sensory information to their final destinations in the CNS using… o Nerves: Axon bundles in the PNS o Nuclei: Cell bodies located in the CNS o Tracts: Axon bundles in the CNS • Somatic motor portion of the efferent division controls peripheral effectors • Somatic motor commands travel from motor centers in the brain along somatic motor pathways of: o Motor nuclei o Tracts o Nerves • Somatic Nervous System (SNS): Motor neurons and pathways that control skeletal musclesBSC2086 Anatomy & Physiology II Exam #1 Study Guide 2 Sensory Receptors • General Senses – describe our sensitivity to: o Temperature o Pain o Touch o Pressure o Vibration o Proprioception: Monitors the position and movements of skeletal muscles and joints • Sensation: The arriving information from these senses • Perception: Conscious awareness of a sensation • Special Senses o Olfaction: Smell o Vision: Sight o Gustation: Taste o Equilibrium: Balance o Hearing • Special senses are provided by special sensory receptors • Special Sensory Receptors: Located in sense organs (i.e eye or ear) o Protected by surrounding tissues • Receptor specificity – each receptor has a characteristic sensitivity o Your hands don’t smell or taste, your eyes don’t hear, etc. • Receptive field o Area monitored by a single receptor cell o Larger receptive fields make it more difficult to localize a stimulus Interpretation of Sensory Information • Arriving stimulus reaches cortical neurons via labeled line – link between receptor and cortical neuron o Each labeled line carries info about one modality (form) Such as… • Physical force (pressure) • Dissolved chemical • Sound • LightBSC2086 Anatomy & Physiology II Exam #1 Study Guide 3 • Taste, hearing, equilibrium, and vision provided by specialized receptor cells Sensory Receptor Adaptation • Adaptation: Reduction in sensitivity of a constant stimulus o Nervous system quickly adapts to stimuli that are painless & constant Ex) New smells, clothes, earrings • Tonic Receptors: Slow-adapting receptors that are always active o Show little peripheral adaptation Ex) Pain receptors (nociceptors) remind you of an injury long after the initial damage has occurred • Phasic Receptors: Fast-adapting receptors that are normally inactive o Become active for a short time whenever a change occurs o Provide information about the intensity and rate of change of a stimulus Ex) Thermoreceptors detect rapid changes in temperature • Stimulation of a receptor produces action potentials along the axon of a sensory neuron • The frequency & pattern of action potentials contain information about the strength, duration, and variation of the stimulus • Your perception of the nature of that stimulus depends on the path it takes in the CNS Types of Sensory Receptors • Exteroceptors: Provide information about the external environment • Proprioceptors: Report the positions of skeletal muscles and joints o Provide purely somatic sensation o Not located in the visceral organs of the thoracic & abdominopelvic cavities You can’t tell where your spleen, appendix, or pancreas is right now • Interoceptors: Monitor visceral organs and functions • General Sensory Receptors – divided into four (4) types by the nature of the stimulus that excites them o Nociceptors (pain) o Thermoceptors (temperature) o Mechanoreceptors (physical distortion) o Chemoreceptors (chemical concentration) • Nociceptors (Pain Receptors): Free nerve endings with large receptive fields o Branching tips of dendrites o Not protected by accessory structures o Can be stimulated by many different stimuli o Two types of axons: Type A: Large, myelinated fibers • Carry sensations of fast pain (prickling pain) o Ex) Pain caused by injection or a deep cut • Sensations reach the CNS quickly and often trigger somatic reflexes • Relayed to the primary sensory cortex and receive conscious attentionBSC2086 Anatomy & Physiology II Exam #1 Study Guide 4 Type C: Small, unmyelinated fibers • Carry sensations of slow pain (burning & aching pain) • Cause a generalized activation of the reticular formation & thalamus • You become aware of the pain, but only have a general idea of the area affected o Common in: Superficial portions of skin Joint capsules Periostea of bones Walls of blood vessels o May be sensitive to: Temperature extremes Mechanical damage Dissolved chemicals • Ex) Chemicals released by injured cells o Analgesia: Inability to feel pain o Hyperalgesia: Increased sensitivity to pain • Thermoreceptors (Temperature Receptors): Free nerve endings o Located in: Dermis Skeletal muscles Liver Hypothalamus o 3-4x more cold receptors than warm receptors o Temperature sensations conducted along the same pathways as pain sensations o Sent to: Reticular formation Thalamus Primary sensory cortex (lesser extent) • Mechanoreceptors o Sensitive to stimuli that distort their plasma membranes o Contain mechanically-gated ion channels Gates open or close in response to: • Stretching • Compression • Twisting • Other distortions of the membrane o Three (3) classes: Tactile Receptors: Provide the sensations of touch, pressure, and vibration • Touch sensations information about shape & texture • Pressure sensations degree of mechanical distortion • Vibration sensations pulsing or oscillating pressure • Fine touch and pressure receptors…BSC2086 Anatomy & Physiology II Exam #1 Study Guide
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